Article pubs.acs.org/JAFC
Biobased Polymer Composites Derived from Corn Stover and Feather Meals as Double-Coating Materials for Controlled-Release and Water-Retention Urea Fertilizers Yuechao Yang,*,†,‡ Zhaohui Tong,§ Yuqing Geng,† Yuncong Li,*,‡ and Min Zhang† †
National Engineering Laboratory for Efficient Utilization of Soil and Fertilizer Resources; National Engineering & Technology Research Center for Slow and Controlled Release Fertilizers, College of Resources and Environment, Shandong Agricultural University, Taian, Shandong 271018, China ‡ Department of Soil and Water Science, Tropical Research and Education Center, University of Florida, Homestead, Florida 33031, United States § Agriculture and Biological Engineering, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, Florida 32611-0570, United States ABSTRACT: In this paper, we synthesized a biobased polyurethane using liquefied corn stover, isocyanate, and diethylenetriamine. The synthesized polyurethane was used as a coating material to control nitrogen (N) release from polymer-coated urea. A novel superabsorbent composite was also formulated from chicken feather protein (CFP), acrylic acid, and N,N′-methylenebisacrylamide and used as an outer coating material for water retention. We studied the N release characteristics and water-retention capability of the double-layer polymer-coated urea (DPCU) applied in both water and soils. The ear yields, dry matter accumulation, total N use efficiency and N leaching from a sweet corn soil-plant system under two different irrigation regimes were also investigated. Comparison of DPCU treatments with conventional urea fertilizer revealed that DPCU treatments reduced the N release rate and improved water retention capability. Evaluation of soil and plant characteristics within the soil-plant system revealed that DPCU application effectively reduced N leaching loss, improved total N use efficiency, and increased soil water retention capability. KEYWORDS: double-layer polymer-coated urea, corn stover, feather meal, nitrogen release rate, water retention, leaching
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INTRODUCTION The Food Agriculture Organization (FAO) has reported that worldwide total fertilizer consumption was about 170.7 million tons in 2011.1 Total fertilizer consumption is projected to reach 190.4 million tons by the year of 2015, based on a growth rate of 2% per year.2 Crop production and landscape management have used, and require, large amounts of fertilizer. These land-use practices have encountered environmental challenges, due to low fertilizer use efficiency and subsequent nutrient release into surface or groundwater, and emission of gases into the atmosphere.3−5 Application of slow and controlled release fertilizers is an effective technique to enhance fertilizer use efficiency.6 Synthetic organic materials have been used to coat urea and other conventional fertilizers and are commonly referred to as polymer-coated fertilizers (PCFs). These PCFs have shown great potential to increase fertilizer use efficiency and crop yield.7 Petroleum-based, synthetic materials, such as polyolefins, polystyrene, dicyclopentadiene, polysulfone, and glycerol ester have also been investigated as potential coating materials for PCFs. 8−10 The manufacturing costs of PCFs are still considerably high, limiting their use to mostly high-value crops.11 Organic solvents are used to dissolve these polymers during the coating process, and most of these solvents are relatively expensive and toxic,12 which limits the commercialization of PCFs. Currently, another problem for the application of PCFs coating materials derived from nonrenewable and © 2013 American Chemical Society
nonbiodegradable materials is that they can accumulate in soil, degrade soil fertility and possibly release toxic gases during the coating degradation process.13 The development of inexpensive, nontoxic, renewable, and biodegradable PCFs for slow- and controlled-release fertilizers will help not only to increase fertilizer use efficiency but also to reduce environmental impacts and costs associated with PCF application.14−16 Although renewable and biodegradable materials, such as lignin, cellulose, chitin, keratin, and starch can be directly used or modified as the coating materials for fertilizers,17−20 when these biobased, renewable materials are used to coat PCFs, the longevity of nutrient release is short, often 2 mm), 19.9% sand, 12.5% silt, and 8.8% clay, and the pH was 7.9. The water-holding capacity was measured for three different treatments: a control, 200 g of dry soil, 200 g of dry soil mixed with 2.0 g of DPCU, and 200 g of dry soil mixed with 4.0 g of DPCU. Soil with uncoated was not included in treatments because uncoated urea had little effect on the water-holding capacity of soil. Each sample was placed in an acrylic tube with an inside diameter of 5 cm. The bottom of the tube was sealed with three layers of 200-mesh nylon fabric and weighed (Ws). The bottom of the tube was submerged in deionized water at room temperature for 24 h. The tube was then removed from the water for 8 h, and the tube was weighed again (Ww). The water holding capacity, as a weight percent (%) of dry soil, was calculated as: (Ww − Ws)/Ws × 100. The water retention rate of DPCU was measured for three different treatments: a control, 2.5 kg of dry soil; 2.5 kg of dry soil mixed with 10.0 g of DPCU; and 2.5 kg of dry soil mixed with 20.0 g of DPCU. Three replicates were measured for each treatment. Soil samples were packed in an acrylic column, and the bottom of the column was sealed with three layers of 200mesh nylon fabric and weighed (M0). The bottom of the soil column was placed in deionized water for 24 h at room
Table 1. The Composition of Various Coated Fertilizers and Water Absorbency (WA) of DPCUs fertilizers
inner coating of LCS-PU (%)
PCU1 PCU2 PCU3 DPCU1 DPCU2 DPCU3
3.2 5.3 8.5 3.2 5.3 8.5
outer coating of MCFP−AA (%)
proportion of the total coating (%)
total N (%)
WA (g/g)
8.7 8.4 8.7
3.2 5.3 8.5 11.9 13.7 17.2
44.5 43.6 42.0 40.5 39.6 38.0
47.7 46.1 48.1
Preparation of DPCU. The DPCU was prepared by first adding 1 kg of PCU into a rotating drum and heating at 50 °C for 10 min. Then ∼10 g of the MCFP−AA solution was added to the surface of the rotating PCU prills as an adhesive. The outer coating was then adhered to the surface of the PCU granules by adding 100 g of the MCFP−AA powder (
